The present invention relates to a finder optical system for single lens reflex (SLR) cameras, and more particularly to a finder optical system for a single-lens reflex camera using an image capturing element such as a CCD (Charge Coupled Device) instead of a photographing film.
Conventionally, an SLR camera has been widely used. In the SLR camera, light passed from a photographing lens is introduced to a finder optical system. Recently, SLR cameras using an image capturing element such as a CCD have been developed and become widespread. In such an SLR camera (i.e., a digital SLR camera), since the area of an image receiving surface of the CCD is relatively small, an image formed by a photographing optical system should be made smaller in comparison with a case where the image is formed on the photographing film.
If the SLR camera is configured such that the image formed on the CCD is small, an image observed through a finder is also small. Therefore, in order to retain a sufficient size of an object image, a magnification of the finder optical system should be sufficiently high.
Recently, the digital cameras are required to be downsized. Therefore, in order to make a structure of the digital camera simple and compact, the finder optical system is also required to achieve the high magnification, and to have an appropriate positional relationship with respect to the other components such as a strobe unit to meet the requirement for downsizing.
It is therefore an object of the invention to provide an improved finder optical system which has a sufficiently high finder magnification and is arranged to have an appropriate positional relationship with respect to the other components of the camera.
For the above object, according to an aspect of the invention, there is provided a finder optical system for a single lens reflex camera, which is provided with a photographing optical system, light from an object being converged by the photographing optical system, an Image of the object being formed on an imaging surface, an optical element inserted in an optical path of the converging light emerged from the photographing optical system, the optical element splitting light passed through the photographing optical system into first light which is deflected by the optical element and second light which passes through the optical element, the first light forming a primary image at a position downstream from the optical element, the second light being incident on the imaging surface to form an object image, a relaying optical system arranged on an optical path of the light deflected by the optical element, the relaying optical system relaying the primary image to form a secondary image, an eyepiece optical system through which the secondary image is observable, and a first reflection surface arranged between the relaying optical system and the eyepiece optical system, the first reflection surface deflecting light, which is directed from the relaying optical system toward the eyepiece optical system, to proceed in a direction parallel with an optical axis of the photographing optical system. In this structure, the secondary image is formed between the first reflection surface and the eyepiece optical system.
Since the secondary image is formed between the first reflection surface and the eyepiece optical system, the magnification of the finder system can be made greater with a compact structure.
optionally, the finder optical system may further include a second reflection surface arranged between the relaying optical system and the first reflection surface, the second reflection surface deflecting light emerged from the relaying optical system toward the first reflection surface, and a third reflection surface arranged between the optical element and the relaying optical system. The third reflection surface deflects the first light deflected by the optical element In a direction inclined with respect to a plane including the first light deflected by the optical element and the optical axis of the objective optical system. The light deflected by the second reflection surface and directed toward the first reflection surface is substantially parallel with the light which is deflected by the optical element and directed to the third reflection surface.
The finder optical system may satisfy the following condition:
80xc2x0xe2x89xa6xcex81xe2x89xa6100xc2x0,
wherein, xcex81 represents an angle formed between the first light deflected by the optical element and the optical axis of the photographing lens.
Optionally, the finder optical system may satisfy the following condition:
55xc2x0xe2x89xa6xcex82xe2x89xa6100xc2x0
wherein, xcex82 represents an angle formed between the optical path of the first light deflected by the optical element and the optical path of the light reflected by the third reflection surface.
Further optionally, each of the first, second, and third reflection surfaces is a surface of a mirror.
Still optionally, the finder optical system may further include a condenser lens arranged between the optical element and the third reflection surface, the finder optical system satisfying the following condition:
0.1xc3x97fe less than d
wherein, fe represents a composite focal length of the relaying optical system and the eyepiece optical system, and wherein d represents a distance between a first focal plane, on which the primary image is formed, and a first focal plane side surface of the condenser lens.
The finder optical system may also satisfy the following condition:
xe2x88x921.4 less than M less than xe2x88x920.7
wherein, M represents a composite magnification of the condenser lens and the relaying optical system.
Furthermore, the imaging surface may be an image receiving surface of an image capturing element.
According to another aspect of the invention, there is provided a camera, which is provided with a camera body having a substantially rectangular parallelepiped shape, a photographing optical system, light from an object being converged by the photographing optical system, an image of the object being formed on an imaging surface, an optical element inserted in an optical path of the converging light emerged from the photographing optical system, the optical element splitting light passed through the photographing optical system into first light which is deflected by the optical element and second light which passes through the optical element, the first light forming a primary image at a position downstream from the optical element, the second light being incident on the imaging surf ace to form an object image, a relaying optical system arranged on an optical path of the light deflected by the optical element, the relaying optical system relaying the primary image to form a secondary image, an eyepiece optical system through which the secondary image is observable, and a first reflection surface arranged between the relaying optical system and the eyepiece optical system, the first reflection surface deflecting light, which is directed from the relaying optical system toward the eyepiece optical system, to proceed in a direction parallel with an optical axis of the photographing optical system. In this structure, the secondary image is formed between the first reflection surface and the eyepiece optical system, and the first light is deflected by the optical element in a direction perpendicular to the optical axis of the photographing lens and parallel with a longer side of the camera.